Subtractive_rng is a Random Number Generator based on the
subtractive method [1]. It is a Unary Function: it takes
a single argument N, an unsigned int, and returns an
unsigned int that is less than N. Successive calls to
the same subtractive_rng object [2] yield a pseudo-random
sequence.
Example
int main()
{
subtractive_rng R;
for (int i = 0; i < 20; ++i)
cout << R(5) << ' ';
cout << endl;
}
// The output is 3 2 3 2 4 3 1 1 2 2 0 3 4 4 4 4 2 1 0 0
Function call. Returns a pseudo-random number in the range
[0, N).
void initialize(unsigned int seed)
subtractive_rng
See below.
New members
These members are not defined in the
Adaptable Unary Function
requirements, but are specific to
subtractive_rng.
Member
Description
subtractive_rng(unsigned int seed)
The constructor. Creates a subtractive_rng whose internal state
is initialized using seed.
subtractive_rng()
The default constructor. Creates a subtractive_rng initialized
using a default value.
void initialize(unsigned int seed)
Re-initializes the internal state of the subtractive_rng, using
the value seed.
Notes
[1]
See section 3.6 of Knuth for an implementation of the subtractive
method in FORTRAN. Section 3.2.2 of Knuth analyzes this class of
algorithms.
(D. E. Knuth, The Art of Computer
Programming. Volume 2: Seminumerical Algorithms, second edition.
Addison-Wesley, 1981.)
[2]
Note that the sequence produced by a subtractive_rng is
completely deterministic, and that the sequences produced by two
different subtractive_rng objects are independent of each other.
That is: if R1 is a subtractive_rng, then the values returned when
R1 is called depend only on R1's seed and on the number of times
that R1 has been called. Calls to other subtractive_rng objects
are irrelevant. In implementation terms, this is because the class
subtractive_rng contains no static members.